Solid-state 13C nuclear magnetic resonance characterization of MDI-based polyurethanes

¹³C solid-state nuclear magnetic resonance (NMR) experiments on linear polyurethanes and poly(ether-urethane) block copolymers demonstrate that ¹³C spin-lattice relaxation experiments in the laboratory [T₁(C)] and rotating [T_1p(C)] frames provide the most information about domain morphology in these microphase-separated polymer systems. T₁(H) TCH, and T_1p(H) data are less useful in a 4,4′-methylene bis(p-phenyl isocyanate)-1,4-butanediol (MDI/BD) hard-segment material, the MDI bridging methylene and the MDI urethane carbonyl T₁(C and T_1p(C) times fall in characteristic ranges for crystalline, amorphous, interfacial, and dissolved species. BD methylene carbons have short T_1p(C) for crystalline and long T_1p(C) for amorphous hard-segment aggregates. The distinct T_1p(C) and T₁(C) fractins observed are attributed to the presence of several crystalline polymorphs. Both T₁(C) results and DSC endotherms indicate that the crystalline polymorphs present in the poly(ether-urethane) are less ordered than the types seen in the pure hard-segment material. © 1993 John Wiley & Sons, Inc.     

On unicyclic conjugated molecules with minimal energies

The energy of a graph is defined as the sum of the absolute values of all the eigenvalues of the graph. Let U(k) be the set of all unicyclic graphs with a perfect matching. Let C _g(G) be the unique cycle of G with length g(G), and M(G) be a perfect matching of G. Let U ⁰(k) be the subset of U(k) such that g(G)≡ 0 (mod 4), there are just g/2 independence edges of M(G) in C _g(G) and there are some edges of E(G)\ M(G) in G\ C _g(G) for any G∈U ⁰(k). In this paper, we discuss the graphs with minimal and second minimal energies in U ^*(k) = U(k)\ U ⁰(k), the graph with minimal energy in U ⁰(k), and propose a conjecture on the graph with minimal energy in U(k).      

Rationalization of the ratio of excimer-to-monomer fluorescence emission intensity in bichromophoric diesters of 1-pyrenoic acid and mono-, di-, tri-, and tetraethylene glycols

The ratio of excimer to monomer emission intensities, denoted by I_D/I_M, was measured for Py–COO(CH₂CH₂O)_mCO ? Py, where Py denotes the 1-pyrenyl group and m = 1–4, in solvents of different viscosity, η. Three different systems were used to change the viscosity of the medium: (a) Mixtures of methanol and ethylene glycol at 25°C, (b) linear aliphatic alcohols, H(CH₂)_nOH, where n =1–6, also at 25°C, and (c) ethylene glycol over the range 6.6–35°C. The ratio I_D/I_M decreases sharply as η increases, and the rate of the decrease in I_D/I_M is a function of m. Quantitatively, the dependence of I_D/I_M on η at high viscosity, i.e., the slope [d(I_D/I_M)/d(1/η)]_∞, is larger in the present work than in another series of 1-pyrenyl diesters in which the flexible spacer is an oligomer of polyethylene, instead of an oligomer of polyoxyethylene. In the limit where η → ∞, the ratio I_D/I_M assumes its largest value in the bichromophoric compound with m = 2. However, as η decreases the compound with m = 3 becomes the one with the largest I_D/I_M. A complete rotational isomeric state analysis (for the compounds with m = 1–3) and a Monte Carlo simulation (for the compound m = 4) of the conformations of the diesters can rationalize the behavior of I_D/I_M in the high viscosity limit. ©1995 John Wiley & Sons, Inc.     

Radial electron-pair densities in momentum space and shell structure of atoms

 The radial electron-pair intracule (relative motion) H(u) and extracule (center-of-mass motion) D(R) densities in position space were known to reveal four types of maxima which are related to the four inner electron shells, K, L, M, and N, of atoms. The corresponding radial electron-pair intracule Hˉ(v) and extracule Dˉ(P) densities in momentum space are studied for the 102 atoms from He (atomic number Z=2) to Lr (Z=103). The densities Hˉ(v) and Dˉ(P) are found to have either one maximum or two maxima, and the numbers of maxima in Hˉ(v) and Dˉ(P) are the same for 98 atoms. For these atoms, the locations υ _max and P _max and the heights Hˉ _max and Dˉ _max of the corresponding maxima satisfy the approximate relations υ _max ≅ 2P _max and Hˉ _max ≅Dˉ _max /2. On the basis of their Z-dependence, the maxima in Hˉ(v) and Dˉ(P) of the 102 atoms are classified into five types. Shell-pair decompositions of the radial densities show that these maxima reflect five outer electron shells of atoms. Received: 24 January 2001 / Accepted: 12 March 2001 / Published online: 13 June 2001     

Diffusion of nonionic azo dyes in nylon-6

Diffusion of 2,4-dinitroaniline and three nonionic azo dyes in Nylon-6 film was studied by analysis of the concentration-distance curves (profiles) of penetrants in the polymer. Actual diffusivities D_(c) of penetrants in polymer, diffusion coefficients as a function of the concentration C_f of penetrant in polymer, were calculated from the profile. It was found that D_(c) is almost constant or decreases gradually with decreasing C_f in the range of high-medium C_f but decreases appreciably with decreasing C_f at low C_f. The change in D_(c) with C_f was explained in terms of the dual-mode sorption-diffusion model. The penetrants diffuse in the polymer as two distinct species, i.e., a dissolved species and an adsorbed species. The former is the penetrant taken up by the polymer by a partition mechanism (dissolved species) and the latter is that taken up by Langmuir sorption (adsorbed species). The actual diffusivity D_P(c) of the dissolved species decreases with decreasing C_f. While the actual diffusivity D_L(c) of the adsorbed species normally increases gradually with decreasing C_f. D_P(c) is usually larger than D_L(c). © 1993 John Wiley & Sons, Inc.     

Molecular van der Waals symmetry affecting bulk properties of condensed phases: melting and boiling points

Qualitative analysis of the trends in melting temperatures T _m and boiling temperatures T _b of organic compounds and related substances supports a concept of van der Waals symmetry suggested earlier by the authors. Data for substituted methanes, ethanes, ethylenes, benzenes and cyclohexanes, reveal linear T _b versus M ^α patterns but usually non-uniform T _m versus M ^α patterns (where M is the molecular mass, α varies from 0.5 to 1). In the same set of isomers, T _m and T _b often change in different succession. To explain the observed trends, a local van der Waals field U that acts on a molecule in a solid or liquid phase, was represented by a sum of an averaged long-range field U ₀ from all molecules, and a short-range “contact” term W determined by a molecular shape. Variations of T _m and T _b among closely related substances correspond to different strength of perturbation of U ₀ ^(C) (in a crystal) and U ₀ ^(L) (in a liquid) by W. Higher T _b of isomers with medium-symmetry molecules (like 1,2-disubstituted benzenes and cyclohexanes) reflect the better fitting of their molecules to a local molecular environment in a liquid (that contains vacancies). Highly symmetrical quasispherical molecules (e.g., C₂Cl₆ or C₆F₁₂) produce a stabilised solid and destabilised liquid state, hence their molecular crystals easily sublime rather than melt at ambient pressure. Dedicated in memory of Professor Petr M. Zorky     

The Synthesis of Hexaphenylcyclotriphosphazene in Improved Yield

The reaction between phenylmagnesium bromide and hexachlorocyclotriphophazene (N ₃ P ₃ Cl ₆ ) ( 1 ) was reinvestigated for the synthesis of hexaphenylcyclotriphosphazene (N ₃ P ₃ Ph ₆ ) ( 2 ) in high yield. The reaction is complete within two weeks at room temperature using toluene as solvent. When the reactants (PhMgBr and N ₃ P ₃ Cl ₆ ) were employed in a 6:1, 36:1 and 72:1 molar ratio, compound 2 was obtained in 2.6%, 14%, and 33.4% yield, respectively. The formation of N ₃ P ₃ Cl ₆ ( 2 ) during the reaction was followed by thin-layer chromatography. Compound 2 was characterized by elemental analysis, IR, UV-VIS, ¹ H, ¹³ C, and ³¹ P NMR spectroscopy as well as by mass spectrometry.     

On the connectivity index of trees

The connectivity index χ₁(G) of a graph G is the sum of the weights d(u)d(v) of all edges uv of G, where d(u) denotes the degree of the vertex u. Let T(n, r) be the set of trees on n vertices with diameter r. In this paper, we determine all trees in T(n, r) with the largest and the second largest connectivity index. Also, the trees in T(n, r) with the largest and the second largest connectivity index are characterized. Mei Lu is partially supported by NNSFC (No. 10571105).     

Entropy Changes in Aqueous Solutions of Non-polar Substances and in Bio-complex Formation

The entropy changes, ΔS _app, (i) for dissolution in water of non-polar substances and (ii) for protein-ligand complexation show linear dependences on the logarithm of the absolute temperature. For every compound, the slope m _(S)=ΔC _p for the line ΔS _app=f(ln T) depends on the size of the molecule and is exactly equal to the slope m _(H)=ΔC _p found in the diagram ΔH _app=f(T). This means that the slopes are rigorously proportional (with a ratio m _(S)/n _w=C _p,w) where n _w is the number of involved water molecules as determined from the enthalpy change ΔH _app=f(T). It is also worth noting that the value of n _w is positive (as well as m _(S) and m _(H)) in the dissolution of non-polar substances, whereas it is negative (as well as m _(S) and m _(H)) in bio-complex formation and in micelle formation. The number n _w (n _w>0) involved in the dissolution of non-polar substances depends on the size of the cavity (excluded volume) formed in the structure of water. These water molecules that have been excluded from the structure of the solvent absorb thermal energy that compensates for the negative enthalpy change, whereas the formation of the cavity implies there should be a large negative entropy contribution. The low solubility of non-polar substances in water depends on the highly negative entropy effect due both to cavity formation and to loss of configurational entropy by the gas trapped in a cage of water molecules. In processes involving association, as in micelle formation and in protein complexation, the cavities surrounding the separate units coalesce and the resultant cavity is smaller than the sum of the previous ones. The n _w water molecules (n _w<0) needed to fill the excess cavity return to the structure of the bulk solvent and release thermal energy, which compensates for the endothermic enthalpy. The affinity in the association processes is bound, for the most part, to the entropy produced by occupation of part of the cavity by condensation of water molecules. The association processes are therefore entropy driven.     

Pharmacokinetics of R‐(−)ondansetron compared with that of S‐(−)ondansetron in rats using an LC–MS/MS method

The pharmacokinetics of R‐(?)ondansetron (R‐ond) compared with that of S‐(?)ondansetron (S‐ond) was studied in rats. R‐ond and S‐ond were injected intravenously into rats at a dose of 2.0 mg/kg. The stability of ondansetron enantiomers in rat was determined by chiral HPLC, and the concentrations of R‐ond and S‐ond in plasma were determined by an LC/MS/MS method. The pharmacokinetic parameters were calculated and analyzed statistically using the t‐test. The enantiomer inversions between R‐ond and S‐ond did not occur in rat. The pharmacokinetic parameters (t_1/2, AUC, MRT, CL) of R‐ond and S‐ond differed significantly. The concentration in plasma of the R/S‐enantiomeric ratio reached a maximum value of 9.5 at 4.0 h post‐dose. The pharmacokinetics of R‐ond and S‐ond are stereoselective in rat, which indicates substantial stereoselectivity in the disposition of ondansetron enantiomers in rat. R‐ond has more potential than S‐ond to be developed as a single enantiomer drug.     

Mono-Heteroatom Effects on Singlet–Triplet Energy Gaps of Divalent Five-Membered Ring XC3H3C (X = CH,N, P,and As)

Heteroatom effects were investigated on singlet–triplet energy gaps of divalent five-membered ring XC ₃ H ₃ C, 1 _X and 2 _X (X = CH, N, P, and As) at B3LYP/6-311++G?? level. All triplet states of 1 _X and 2 _X are more stable than the related singlet state. Δ G _{s ? t} between singlet and triplet states of 1 _X and 2 _X were changed in the order (in kcal/mol): 1 _As (14.43) > 1 _P (10.07) > 1 _CH (9.60) > 1 _N (8.50) and 2 _N (11.56) > 2 _CH (9.60) > 2 _P (3.07) > 2 _As (2.13).     

Electron-pair radial density functions

We introduce and discuss a generalized electron-pair radial density function G(q; a) that represents the probability density for the electron-pair radius |r ₁+ar ₂| to be q, where a is a real-valued parameter. The density function G(q; a) is a projection of the two-electron radial density D ₂(r ₁, r ₂) along lines r ₁ + ar ₂ ± q = 0 in the r ₁ r ₂ plane onto a point in the qa plane, and connects three densities S(s), D(r), and T(t), defined independently in the literature, as a smooth function of a: For an N-electron (N ≥ 2) system, S(s) = G(s; + 1), D(r) = 2G(r; 0)/(N − 1), and T(t) = G(|t|;−1)/2, where S(s) and T(t) are the electron-pair radial sum and difference densities, respectively, and D(r) is the single-electron radial density. Simple illustrations are given for the helium atom in the ground 1s² and the first excited 1s2s ³S states.     

Effects of mechanical and thermal stresses on electric degradation of polyolefins and related materials

Degradation under the simultaneous effects of mechanical stress and temperature in polyolefins (PE, PP), composites on their basis (PE+PP fibre, PP+PP fibre, PP+glass fibre) and radiation low-density polyethylene (X-LDPE) used in high-voltage cables obeys the thermofluctuation theory of Zhourkov (in certain σ and τ₀ intervals) based on the theory of Arrhenius is presented in the following form: τ_σ = τ₀ exp[(U₀ − γσ)/ RT] (1) where τ is durability. τ₀ is a constant (10⁻¹²-10⁻¹³s) equal to period of vibrations of atoms around equilibrium position, U₀ is the activation energy of the mechanical destruction process (at σ = 0), γ is a structure-sensitive parameter, T is absolute temperature and R is universal gas constant. Electric degradation under the effects of electric field and temperature in the materials mentioned above obeys the equation: τ_E = τ₀ exp[(W₀ − χE)/ RT] (2) Here, τ_E, W₀ and χ are analogous to τ_σ, U₀ and γ, respectively. It is assumed that the following equation is valid under the simultaneous effects of E, σ and T: τ_σ,E = τ₀ exp[(U₀ − (γσ + χE))/ RT]. (3) electric degradation     

Preparation of C2‐Symmetric Bis[2‐(diphenylphosphino)ferrocen‐1‐yl]‐ methane and Its Use in Rhodium‐ and Ruthenium‐Catalyzed Hydrogenation

The two diphosphine ligands (R_p,R_p)‐ and (S_p,S_p)‐bis[2‐(diphenylphospino)ferrocenyl]methane, (R_p,R_p)‐ and (S_p,S_p)‐ 1 , resp., were prepared in six steps from (S)‐ and (R)‐ferrocenyl tolyl sulfoxide, respectively (Scheme). In the solid state, both the diborane complex (R_p,R_p)‐ 1 ? (BH₃)₂ and the palladium dichloride complex [PdCl₂((R_p,R_p)‐ 1 )] were found to adopt C₂‐pseudosymmetric structures according to X‐ray analyses (Figs. 2 and 3). In the Rh‐ and Ru‐catalyzed hydrogenation of selected alkenes and ketones in the presence of the new ligands, enantioselectivities of up to 55% ee were obtained.     

NMR‐Solution Structures of Fluoro‐Substituted β‐Peptides: A 314‐Helix and a Hairpin Turn. The First Case of a 90° OC?C?F Dihedral Angle in an α‐Fluoro‐Amide Group

To further study the preference of the antiperiplanar (ap) conformation in α‐fluoro‐amide groups, two β‐peptides, 1 and 2 , containing a (2‐F)‐β³hAla and a (2‐F)‐β²hPhe residue, have been synthesized. Their NMR‐solution structures in CD₃OH were determined and compared with those of non‐F‐substituted analogs, 3 and 4a . While we have found in a previous investigation (Helv. Chim. Acta 2005 , 88, 266) that a stereospecifically introduced F‐substituent in the central position of a β‐heptapeptide is capable of ‘breaking’ the 3₁₄‐helical structure by enforcing the F? C? C?O ap‐conformation, we could now demonstrate that the same procedure leads to a structure with the unfavorable ca. 90° F? C? C?O dihedral angle, enforced by the 3₁₄‐helical folding in a β‐tridecapeptide (cf. 1 ; Fig. 4). This is interpreted as a consequence of cooperative folding in the longer β‐peptide. A F‐substituent placed in the turn section of a β‐peptidic hairpin turn was shown to be in an ap‐arrangement with respect to the neighboring C?O bond (cf. 2 ; Fig. 7). Analysis of the non‐F‐substituted β‐tetrapeptides (with helix‐preventing configurations of the two central β²/β³‐amino acid residues) provides unusually tight hairpin structural clusters (cf. 3 and 4a ; Figs. 8 and 9). The skeleton of the β‐tetrapeptide H‐(R)β³hVal‐(R)β²hVal‐(R)β³hAla‐(S)β³hPhe‐OH ( 4a ) is proposed as a novel, very simple backbone structure for mimicking α‐peptidic hairpin turns.     

Twisted Baskets

A preparative procedure for obtaining a pair of twisted molecular baskets, each comprising a chiral framework with either right ((P)‐ 1 _syn) or left ((M)‐ 1 _syn) sense of twist and six ester groups at the rim has been developed and optimized. The racemic (P/M)‐ 1 _syn can be obtained in three synthetic steps from accessible starting materials. The resolution of (P/M)‐ 1 _syn is accomplished by its transesterification with (1R,2S,5R)‐(?)‐menthol in the presence of a Ti^IV catalyst to give diastereomeric 8 ^P and 8 ^M . It was found that dendritic‐like cavitands 8 ^P and 8 ^M , in CD₂Cl₂, undergo self‐inclusion (¹H NMR spectroscopy) with a menthol moiety occupying the cavity of each host. Importantly, the degree of inclusion of the menthol group was (¹H NMR spectroscopy) found to be greater in the case of 8 ^P than 8 ^M . Accordingly, it is suggested that different folding characteristic of 8 ^P and 8 ^M ought to affect the physicochemical characteristics of the hosts to permit their effective separation by column chromatography. The absolute configuration of 8 ^P/ 8 ^M , encompassing right‐ and left‐handed “cups”, was determined with the exciton chirality method and also verified in silico (DFT: B3LYP/TZVP). Finally, the twisted baskets are strongly fluorescent due to three naphthalene chromophores, having a high fluorescence quantum yield within the rigid framework of 8 ^P/ 8 ^M .     

Mass transfer in the gas phase during top-blowing with plasma jets

Deoxidation of copper melts by hydrogen has been investigated experimentally by top-blowing with argon-hydrogen plasma jets. The course of the deoxidation process has been described mathematically using kinetic laws. The overall divided course of the process can be examined in live partial steps, which are hydrogen transport within the gas phase, hydrogen transport within the melt, oxygen transport within the melt, reaction between hydrogen and oxygen, and H₂O transport within the gas phase. Based on these five elementary processes, an equation for the velocity of deoxidation has been derived. The values of the rate of deoxidation resulting from this equation, in combination with the mass-transter coefficients valid for this process, have been compared to the experimental data. The results of this study verify those of former investigations on vaporization of elements out of copper melts. The mass-transfer coefficients are the same, when the local activity differences are used as the driving force for mass transport in a system. This means that the surface-renewal theory is valid, when mass-transfer coefficients are defined in this way. This is the case, at least, when metallic melts are subjected to top-blowing by plasma jets.Nomenclature a activity (a _i =x _{i i} ) - A _c (m²) effective mass-transfer area - D(m) characteristic length, such as diameter - D _r(m²/s) diffusion coefficient - H(Cu) oxygen dissolved in copper - k _g (mol/m²s) mass-transfer coefficient in the gas phase [k _g (i) mass-transfer coefficient for speciesi] - k _N (mol/m²s) mass-transfer coefficient in the melt phase - K _i = (x _i /y _i )_eq equilibrium coefficient (distribution coefficient) - n _N (mol) mole number of the melt phase - n _G (mol) mole number of the gas phase - n _i (mol/s) mole flow of speciesi - O(Cu) oxygen dissolved in copper - p(N) momentum flow - t(s) time - T (°C or K) temperature;T _G : in the gas,T _s : in the melt,T ^f : at the phase interface - x _i (mol/mol) concentration in the melt - y _i , (mol/mol) concentration in the gas phase - activity coefficient     

CAROTENE AND CYTOCHROME c DEPENDENT MITOTIC RECOMBINATION AND KILLING IN RESPONSE TO VISIBLE LIGHT AND UV-C IN THE SMUT FUNGUS Ustilago Violacea

Abstract— The carotene (carotenoid hydrocarbons) and cytochrome c compositions for the phlph⁺ pink diploid strain of Ustilago violacea and three newly developed color variants, white (w), orange (o), and yellow (y) were quantitatively determined using high-performance liquid chromatography of lipid extracts and difference spectroscopy of alkali extracts. In addition, the effect of high-intensity incandescent and far UV (UV-C) radiation on survival and mitotic recombination in all four phlph⁺ strains were studied. The phlph⁺w and phlph⁺y strains contained relatively small amounts of cytochrome c; however, the phlph⁺y strain accumulated β-carotene while in the phlph⁺w strain only the colorless carotene phytoene was found. The phlph⁺w was very sensitive to incandescent radiation, with complete killing by 90 min of exposure. The induction of mitotic recombination in the phlph⁺w strain was inversely proportional to the level of survival, with 96% induction by 90 min of exposure. The β-carotene-accumulating phlph⁺y strain was considerably more resistant to photokilling, and exhibited induction of mitotic recombination at a lower level. Similar results were observed with these strains in response to UV-C. The phlph⁺y strain was significantly more resistant to UV-C killing than the phlph⁺w strain and it also exhibited lower induced levels of mitotic recombination. The phlph⁺o and phlph⁺ pink strains accumulated over 10 times the cytochrome c as the phlph⁺w or phlph⁺y strains. The phlph⁺o strain accumulated β-carotene at the level of the phlph* y strain, but the phlph⁺ pink strain contained only about one-tenth as much β-carotene. The phlph⁺ o and phi ph⁺ pink strains exhibited sensitivity to visible radiation that was intermediate to the phlph⁺y and phlph⁺w strains. Mitotic recombination induction by visible radiation in the orange and pink strains was slightly less than that in the phlph⁺w strain. In response to UV-C, the phlph⁺o and phlph⁺ pink strains had survival and mitotic recombination induction characteristics that were similar to the phlph⁺w strain.     

Nine New Sesquiterpenes from Dendrobium nobile

Nine new sesquiterpenes, i.e., dendronobilins A–I ( 1 – 9 ), with copacamphane‐type ( 1 ), picrotoxane‐type ( 2 – 6 ), muurolene‐type ( 7 ), alloaromadendrane‐type ( 8 ), and cyclocopacamphane‐type ( 9 ) skeletons, were isolated from the 60% EtOH extract of the stems of Dendrobium nobile. Their structures were established as (1R,2R,4S,5S,6S,8S,9R)‐2,8‐dihydroxycopacamphan‐15‐one ( 1 ), (2β,3β,4β,5β)‐2,4,11‐trihydroxypicrotoxano‐3(15)‐lactone ( 2 ), (2β,3β,5β,9α,11β)‐2,11‐epoxy‐9,11,13‐trihydroxypicrotoxano‐3(15)‐lactone ( 3 ), (2β,3β,5β,12R*)‐2,11,13‐trihydroxypicrotoxano‐3(15)‐lactone ( 4 ), (2β,3β,5β,12S*)‐2,11,13‐trihydroxypicrotoxano‐3(15)‐lactone ( 5 ), (2β,3β,5β,9α)‐9,10‐cyclo‐2,11,13‐trihydroxypicrotoxano‐3(15)‐lactone ( 6 ), (9β,10α)‐muurol‐4‐ene‐9,10,11‐triol ( 7 ), (10α)‐alloaromadendrane‐10,12,14‐triol ( 8 ), and (5β)‐cyclocopacamphane‐5,12,15‐triol ( 9 ) on the basis of spectroscopic analysis. The absolute configuration of compound 1 was tentatively assigned as (1R,2R,4S,5S,6S,8S,9R) according to its CD spectrum and the octant rule. Compounds 1 and 4 – 9 were inactive in our preliminary in vitro immunomodulatory bioassay.     

Volume and enthalpy relaxation response after combined temperature history in polycarbonate

Summary Volume and enthalpy relaxation in polycarbonate subjected to double temperature jumps in the T_g region has been analysed. It concerns both initial T_down-jump from equilibrium above T_g to consolidation temperature below T_g and fina1 T_up-jump to relaxation temperature, also below T_g. The measured H and V data after T_up-jump were compared with respect to aging time calculating (dH/dV) ratio denoted as aging bulk modulus, K_a. According this new methodology H and V relaxation response after T_up-jump demonstrates differences in relaxation responses.